Not humanoids. There is a condition where the spine develops a supposed tail with humans. They've called it evolution. The tail bone protrudes, as a birth defect. It affects very rarely, so rare in 100s of million, very few cases. It must be removed, or it can cause obvious injury. Basically the tail bone in the butt, grows by a few inches sticking out of the butt. Imagine sitting down, don't. It has affected primarily Asian populations mysteriously.

Not on creatures that stand up. Unless you count, meerkats, and monkeys, limurs, etc, using mostly 4 limbs to walk. Spending more time in trees and whatever.

That has no fucking use. If you stand, evolution, you lose the tail, unless you have monkey syndrome. Hahaha.